System and method for washing articles employing a densified cleaning solution, and use of a fluid displacement device therein

ABSTRACT

A dry cleaning system arranged for washing articles employing a cleaning solution. The dry cleaning system includes awash tank ( 2 ) for washing an article to be washed with a cleaning solution. The wash tank ( 2 ) is arranged for washing the article at an increased pressure compared to atmospheric pressure. The dry cleaning system includes a fluid displacement device ( 1 ), such as a pump, connected to the wash tank ( 2 ) and is arranged for transferring the cleaning solution through the dry cleaning system in a first operational mode. The fluid displacement device is arranged to reduce the pressure in the wash tank towards atmospheric pressure in a second operational mode.

FIELD OF THE INVENTION

The invention relates to systems and methods for conserving vapor andcollecting liquid carbon dioxide for cleaning systems, more particularlyto methods and systems for conserving vapor and collecting liquid carbondioxide for carbon dioxide dry cleaning systems.

BACKGROUND OF THE INVENTION

Dry cleaning systems are known. Additionally, dry cleaning systems thatuse vapor and liquid carbon dioxide are known. The system employs awashing vessel, in which articles to be washed may be placed. Vapor andliquid carbon dioxide is transferred to the washing vessel. The carbondioxide is pressurized inside the washing vessel. Pressures inside thevessel may be equal to approximately 700-900 psi. Liquid and vaporcarbon dioxide is capable of cleaning the articles. Additives, such asorganic solvents, may be supplemented. After washing, the washing vesselis depressurized. Liquid and vapor carbon dioxide are removed from thewashing vessel. The clothes may be removed from the washing vessel,after which a new washing cycle may be initiated.

A drawback of the known systems and methods is loss of vapor carbondioxide. Blow off of vapor carbon dioxide for depressurizing the washingvessel leads to losses of material. Additionally, in other parts of thesystems, i.e. in piping systems and connections thereof, losses ofcarbon dioxide may occur. The loss of this carbon dioxide needs to bereplenished in a new washing cycle. Additionally, the losses of liquidand vapor carbon dioxide are associated with a relatively lowthermodynamic efficiency.

SUMMARY OF THE INVENTION

It can therefore be an object of the present invention to providesystems and methods for minimizing the losses of carbon dioxide in aliquid carbon dioxide dry cleaning system.

It can be another object of the present invention to provide systems andmethods for improving the thermodynamic efficiency of liquid carbondioxide dry cleaning systems.

It can be a further object of the present invention to provide systemsand methods for lowering the capital costs associated with a liquidcarbon dioxide dry cleaning system.

The present invention provides a dry cleaning system arranged forwashing articles employing a cleaning solution. The system comprises awash tank for washing an article to be washed with a cleaning solution.The wash tank may be arranged for washing the article at an increasedpressure compared to atmospheric pressure (hyperatmospheric pressure).The system may comprise a fluid displacement device, such as a pump,connected to the wash tank and arranged for transferring the cleaningsolution through the dry cleaning system in a first operational mode.According to the invention, the fluid displacement device may be used toreduce the pressure in the wash tank towards atmospheric pressure in asecond operational mode. Instead of blowing off the contents of the washtank, these contents are kept in the dry cleaning system. Loss ofmaterial is thus prevented. Additionally, loss of heat is prevented. Thefluid displacement device, being arranged for both transferring cleaningsolution, as well as depressurizing the wash tank, ensures that arelatively simple dry cleaning system having a minimal amount ofcomponents may be used. The complexity of the system is reduced.Connections between the components (e.g. fluid displacement device andwash tank) may be relatively simple. This reduces the losses of cleaningsolution, and more specifically losses of carbon dioxide in the system,for instance losses that occur at connections in the system. The reducedcomplexity of the system also lowers capital costs.

The washing tank may be arranged for washing articles at a pressure ofapproximately 700-900 psi, for instance 715 psi or 875 psi. It should benoted however, that higher or lower pressures are thinkable. Thecleaning solution may be a densified cleaning solution. The cleaningsolution may comprise a vapor and a liquid, such as vapor and liquidcarbon dioxide.

In an embodiment, the dry cleaning system may comprise adepressurization unit connected to the wash tank for reducing thepressure in the wash tank towards atmospheric pressure. Thedepressurization unit may be a valve. The depressurization unit, i.e.the fluid displacement device, may be used to accurately control thepressure inside the wash tank. Preferably, however, the depressurizationunit is the fluid displacement device. The contents of the wash tank maybe preserved in the dry cleaning system, preventing loss of material.

It is possible that the fluid displacement device is arranged forremoving vapor from the wash tank in the second operational mode. Afterwashing, liquid cleaning solution may be removed from the wash tank bymeans of the fluid displacement device operating in the firstoperational mode. Vapor cleaning solution will remain in the wash tank.Pressures inside the wash tank will still be elevated compared toatmospheric pressure. The fluid displacement device may be arranged fordraining the contents, such as a vapor or a gas, e.g. vapor carbondioxide, from the wash tank. With this, the pressure inside the washtank may be reduced towards atmospheric pressure. The contents drainedmay be re-used in the system. With this, preservation of cleaningsolution, e.g. carbon dioxide, may be exerted, minimizing losses ofmaterial, and additionally increasing thermodynamic efficiency.

In an embodiment, the fluid displacement device is arranged forcompressing vapor removed from the wash tank. The pressure of the vaporremoved may be brought to a desired level. For instance, the pressuremay be increased to the working pressure of the system. With this, thevapor removed may be brought to a pressure suitable for use in the drycleaning system, e.g. for use in a new washing cycle. This ensures thatthe pressure throughout the system, except for the wash tank, may bekept at a uniform level. Pressure losses in the system are reduced. Withthis, thermodynamic efficiency may be increased. In the wash tank, thepressure may be reduced such that articles that are washed may beremoved from the wash tank. The fluid displacement device may be used asa compressor, and may increase the pressure of the vapor removed toapproximately, for instance, 715 psi or 875 psi. Other pressures, suchas higher or lower pressures, are, of course, also possible.

The fluid displacement device may be a pumping/compressing unit arrangedfor pumping and compressing the cleaning solution. In a first operatingmodus, the fluid displacement device may be used for pumping cleaningsolution in liquid form throughout the system. In a second operatingmodus, the displacement device may be used for pumping cleaning solutionin vapor form throughout the system. In the second operating modus, thefluid displacement device may additionally be used to increase thepressure of the vapor. The combination of two operating modes in onefluid displacement device may lead to lower capital costs.

In an embodiment, the fluid displacement device is apositive-displacement device. The positive-displacement device may be areciprocating device or a piston device that uses one or more pistonsdriven by a crankshaft to pressurize fluid. The use of apositive-displacement device with one or more pistons enables the use ofa single fluid displacement device for transferring fluids, such asliquids and vapors, as well as compressing fluids, and more particularlyfor compressing vapors.

In an embodiment, the fluid displacement device comprises an inletconnected to a pumping chamber, in which a piston is reciprocallymovable. The pumping chamber may comprise a pumping chamber inletopening connected to the inlet. The pumping chamber may also comprise apumping chamber outlet opening connected to the outlet. The pumpingchamber comprises a discharge unit connected to the pumping chamberoutlet opening. The discharge unit is arranged for closing the pumpingchamber outlet opening when a pressure inside the pumping chamber isless than a pre-set pressure. With this it is possible to compressvapor, and to transfer liquid. The fluid displacement device may thusact as a pumping/compressing unit.

The pumping chamber inlet opening may be provided near one end of thepumping chamber, and the pumping chamber outlet opening may be providednear an opposite end. This way, the piston may be used to close thepumping chamber inlet opening There is no need for a complicated andexpensive system for closing the pumping chamber inlet opening during acompression stroke of the fluid displacement device.

In an embodiment, the discharge unit is a spring-loaded valve. Thedischarge unit ensures that the fluid, such as a gas or a vapor, may becompressed in order to increase the pressure of the fluid. The fluiddisplacement device is able to function as a pumping/compressing unit,arranged for both pumping and compressing the cleaning solution.

It is possible that the fluid displacement device comprises additionalpumping chambers connected to the inlet and the outlet. The pumpingchamber comprises a pumping chamber inlet, a pumping chamber outlet, apiston. An additional discharge valves may be provided. The pumpingchambers of the fluid displacement device are used for both pumping andcompressing fluid. In other words, the pumping chambers have differentfunctions, in different modi of the fluid displacement device. It ispossible that the positive displacement device comprises at least threepumping chambers, connected to a single inlet, and connected to a singleoutlet. With this, the fluid displacement device may exert effectivepumping and compressing.

The dry cleaning system may further comprise a central storage tank forstoring the cleaning solution. The central storage tank enables storageof unused cleaning solution. The fluid displacement device may be usedto transfer cleaning solution from the central storage tank, to the washtank, and vice versa.

In an embodiment, the dry cleaning system may comprise a first pipingsystem arranged for bringing the central storage tank into fluidcommunication with the wash tank. The first piping system may be used totransfer liquid carbon dioxide from the central storage tank to the washtank. Transfer from the wash tank to the central storage may also bepossible. Transfer may be exerted by the fluid displacement device. Thefluid displacement device may function as a pump for the first pipingsystem. The system may further comprise a second piping system arrangedfor bringing the wash tank into vapor communication with the centralstorage tank. The second piping system may be used to transfer vaporfrom the wash tank to the central storage tank. Transfer from thecentral storage tank to the wash tank may also be possible. The systemmay further comprise a common piping system formed by a coinciding partof the second piping system and the first piping system. This way, thecommon piping system may be used for separate transfer of both liquids,and vapors, enabling the fluid displacement device to work in twooperating modes. Preferably, the fluid displacement device is residingin the common piping system. The common piping system improves thermalefficiency, since losses to the environment are minimized. Also, costsare decreased.

It is possible that the dry cleaning system comprises an intermediatestorage tank for temporarily storing the cleaning solution. Theintermediate storage tank may be connected to the wash tank. The fluiddisplacement device may be arranged for transferring the cleaningsolution between the cleaning device and the wash tank. The intermediatestorage tank allows for already used cleaning solution, which may bere-used again, to be stored for further use. The intermediate storagetank may be used for storing liquid cleaning solution. The intermediatestorage tank may be connected to the first piping system. It is possiblethat used cleaning solution, which is dirty, is used again in the sameor any further washing cycle. The intermediate storage ensures that thiscleaning solution may be stored for further use, without affecting thecleaning solution in the central storage tank.

It is possible that the dry cleaning system comprises a cleaning devicefor cleaning the cleaning solution. The cleaning device may be connectedto the wash tank. The fluid displacement device may be arranged fortransferring the cleaning solution to the cleaning device. Already usedcleaning solution may be cleaned using this device. The cleaningsolution may, after having been cleaned, be transferred to the centralstorage tank. The cleaning device may be part of the common pipingsystem, such that both vapor and liquid cleaning solution may becleaned.

In an embodiment, the fluid displacement device is arranged forcompressing vapor cleaning solution, and transferring compressed vaporto the cleaning device.

In an embodiment, the cleaning device is a distillation unit. Thedistillation unit may be used to distillate the used and relativelydirty cleaning solution. Distillation of the already used cleaningsolution ensures that impurities are removed. Distillation is relativelysimple. Distillation also has a relatively high efficiency. Distillationensures that a relatively clean cleaning solution may be obtained, whichcleaning solution may be re-used in a further washing cycle.

The system may further comprise a central storage tank for storing thecleaning solution. The central storage tank may be connected to the washtank. The distillation unit may be connected to the central storage tankfor returning cleaned cleaning solution to the central storage tank. Thesystem may comprise a third piping system arranged for bringing thedistillation unit into fluid connection with the central storage tankfor returning relatively clean cleaning solution to the central storagetank. This way, used cleaning solution may be cleaned and transferred tothe central storage tank, after which it may be used in a next washingcycle.

The system may comprise a cooling unit arranged for bringing the cleanedand returned cleaning solution into liquid form. The cooling unit mayreside in the third piping system. Preferably, the cleaning solution isreturned to the central storage tank in liquid form. During thedistillation process, the cleaning solution will evaporate. The vaporcleaning solution may then be transferred through the third pipingsystem, for instance under the influence of buoyancy forces, to thecentral storage tank. To bring the vapor into liquid form, the vapor maybe cooled using the cooling unit.

Preferably, the cleaning solution comprises liquid carbon dioxide. Thecarbon dioxide, when used in a dry cleaning system, producessatisfactory results. As stated before, additives, such as organic orinorganic solvents, may be present in the cleaning solution.

In an embodiment, a purging unit is provided for cleaning the wash tank.The purging unit may be part of the dry cleaning system. The cleaning ofthe wash tank is preferably exerted before the start, or at thebeginning of a new wash cycle. The purging unit may be arranged forremoving nitrogen and oxygen from the wash tank.

The purging unit may comprise a purge tank for storing a purging fluid,wherein the purge tank may be brought into fluid communication with thewash tank, and wherein the purging fluid is arranged for cleaning thewash tank.

In an embodiment, the purging fluid is vapor carbon dioxide. Thepressure of the purging fluid may be in between 72 and 230 psi. Thepurging fluid efficiently removes air, and more specifically nitrogenand oxygen, from the wash tank.

The dry cleaning system may comprise a central storage for storing vaporcleaning solution. The vapor cleaning solution may be vapor carbondioxide. The central storage may be connected to the wash tank fortransferring vapor cleaning solution to the wash tank. The dry cleaningsystem may further comprise a further piping system arranged forbringing the central storage tank into vapor communication with the washtank. Preferably, the further piping system may be used to transfervapor cleaning solution from the central storage tank to the wash tank.

In an embodiment, a central storage for both vapor and liquid cleaningsolution is provided.

According to another aspect of the invention, a method for washing anarticle in a dry cleaning system employing a cleaning solution isprovided. The cleaning solution may be a densified cleaning solution.The system comprises a wash tank for washing an article to be washedwith the cleaning solution, and a fluid displacement device connected tothe wash tank and arranged for transferring the cleaning solution. Themethod comprises the step of operating the fluid displacement device fortransferring the cleaning solution in the dry cleaning system, andoperating the same fluid displacement device for depressurizing the washtank. The fluid displacement device may be used for transferring liquidcleaning solution throughout the dry cleaning system. Additionally, thesame fluid displacement device may be used for depressurizing the washtank after washing. Instead of blowing off the contents of the washtank, the contents may be re-used. This way, loss of material isprevented. Furthermore, in the method only a single component is usedfor providing two functions to the dry cleaning system.

The step of operating the same fluid displacement device fordepressurizing the wash tank may comprises the step of reducing thepressure in the wash tank towards atmospheric pressure. The pressure inthe wash tank may be reduced from approximately 700-800 psi, toapproximately 100-200 psi, in a relatively controlled manner. With this,pressure is reduced towards atmospheric pressure. Additionally, afurther reduction to approximately 14.7 psi may be exerted.

The step of operating the same fluid displacement device fordepressurizing the wash tank may comprise the step of removing vaporfrom the wash tank. In the wash tank, vapor cleaning solution, such asvapor carbon dioxide, may be present. The vapor may have a pressure ofapproximately 700-800 psi. Depressurizing of the wash tank may beexerted by the fluid displacement device. This way, the vapor cleaningsolution will remain in the dry cleaning system, and it is thereforepossible to re-use the vapor cleaning solution. For instance, the vapormay be stored temporarily for further use. It is also possible that thevapor cleaning solution is cleaned. Furthermore, it is possible that thevapor cleaning solution is liquefied.

In an embodiment, the step of operating the same fluid displacementdevice for depressurizing the wash tank comprises the step ofcompressing the vapor removed from the wash tank. This way, the pressureof the vapor, which was reduced during the depressurization of the washtank, may be increased to a desired level. For instance, the pressuremay be increased to a relatively constant level. For instance, thepressure may be increased to a constant value in the range of 700-900psi, e.g. 725 psi, or 875 psi. Intermediate values are also possible.The constant value may be dependent on the value used throughout therest of the system. Preferably, the pressure is increased to thepressure needed in the wash tank.

The method may comprise the steps of operating the fluid displacementdevice for pumping the cleaning solution in liquid form; and operatingthe fluid displacement device for compressing the cleaning solution invapor form. The fluid displacement device may thus operate as a pump,for pumping liquids. The fluid displacement device may also operate as acompressor, for transferring and pressurizing vapors.

According to another aspect, a fluid displacement device is used in adry cleaning system for washing articles in a wash tank employing acleaning solution at a hyper-atmospheric pressure, for depressurizingthe wash tank. Instead of blowing off the contents of the wash tank, thecontents are kept in the system, minimizing losses of material.Furthermore, a single device may be used for transferring fluid to thewash tank, and depressurizing the wash tank. Additionally, the use ofsuch a fluid displacement device enables accurate and controlleddepressurization of the wash tank. Furthermore, a relatively simplesystem is provided, since the fluid displacement device may be used intwo operating modes.

According to yet another aspect, a fluid displacement device arrangedfor displacing and compressing fluids is used, in a dry cleaning systemfor washing articles employing a cleaning solution at ahyper-atmospheric pressure. With this, a relatively simple dry cleaningsystem is obtained, since the fluid displacement device may be used intwo operating modes.

The use of the fluid displacement device may comprise compressing thecleaning solution in vapor form. The fluid displacement device may alsooperate as a compressor, for transferring and pressurizing vapors. Withthis, the pressure of the vapor may be increased, whilst the pressure inthe wash tank may effectively be decreased. The pressure throughout therest of the dry cleaning system may remain at a constant level.Therefore, the use ensures that a relatively thermodynamic efficientsystem is obtained. The pressure may be a working pressure. The workingpressure may be a constant value in the range of 700-900 psi, e.g. 725psi or 875 psi. Different values are of course also possible. The fluiddisplacement device may be arranged for compressing vapor cleaningsolution towards the working pressure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a dry cleaning system employing a fluid displacementdevice according to one embodiment of the present invention; and

FIG. 2A, FIG. 2B and FIG. 2C illustrate a fluid displacement deviceaccording to one embodiment of the present invention showing threedifferent positions of an internal piston.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention now will be described hereinafter with referenceto the accompanying drawings, in which a preferred embodiment of theinvention is shown. This invention may, however, be embodied in manydifferent forms and should not be construed as limited to the embodimentset forth herein.

Referring to FIG. 1, a carbon dioxide dry cleaning system is shown. Thesystem comprises a wash tank 2 in which clothes and the like may bebrought for washing, using a liquid/gaseous carbon dioxide cleaningsolution. Besides the wash tank 2, the system comprises additionalcomponents that may be used to obtain a satisfactory washing result, aswill be described next. The wash tank 2 is connected via lines 101, 102to a purge tank 3, from which clean gaseous carbon dioxide may bebrought into the wash tank 2. The wash tank is furthermore connected toan intermediate storage 4, in which liquid carbon dioxide cleaningsolution may be temporarily stored during a washing cycle. The systemfurther comprises a distillation 6 in which liquid carbon dioxidecleaning solution may be brought for cleaning The cleaned solution maybe transferred via lines 110, 111, to a central storage tank 5 forstoring liquid carbon dioxide cleaning solution. The storage tank 5 isconnected to the wash tank 2, such that clean liquid carbon dioxide maybe brought into the wash tank 2 during a washing cycle. The systemfurther comprises a fluid displacement device 1 for transferring theliquid/gaseous carbon dioxide cleaning solution throughout the systemand its various components. The fluid displacement device 1 is arrangedfor both pumping liquid and vapor, and may also be used to compress theliquid and/or vapor, in order to keep the pressure at the pressure sideof the fluid displacement device 1 at a desired level, as will bedescribed later. Several valves 20-32 may be used to connect thedifferent components to each other, as will be explained in furtherdetail below.

In general, the wash cycle comprises the following steps: 0) Providingcarbon dioxide cleaning solution, for instance to a central storage tank5; 1) placing clothes to be cleaned inside the wash tank 2; 2) Chargingcarbon dioxide vapor into wash tank 2 to pressurize it; 3) transferringliquid cleaning solution, comprising liquid carbon dioxide as a solvent,from a general storage vessel (such as central storage tank 5) to thewash tank 2 via fluid displacement unit 1; 4) washing clothes in washtank 2; 5) draining liquid cleaning solution from wash tank 2 to ageneral storage vessel; 6) depressurize the wash tank 2, e.g. byremoving carbon dioxide vapor from the wash tank 2; and 7) removingclean clothes from wash tank 2.

Referring to FIG. 1, the general wash cycle will be described in moredetail. At the beginning of the wash cycle, the wash tank 2 is atatmospheric pressure (14.7 psi).

All valves 21-32 are in a closed position. Clothes to be cleaned may beplaced inside the wash tank 2. Next, the wash tank is pressurized. Thismay be done by connecting the central storage tank 5 to the wash tank 2.In the central storage tank 5, relatively clean cleaning solution, suchas for example liquid and vapor carbon dioxide is stored at a pressureof approximately 725 psi. Higher pressures, such as 875 psi, are ofcourse also possible. The central storage tank 5 is connected to thewash tank through line 104. Line 104 is provided in the part of thecentral storage tank 5 where vapor carbon dioxide accumulates. In thisline, valve 23 is placed. By opening valve 23, an open connectionbetween the storage tank 5 and the wash tank 2 is established. As aresult, vapor carbon dioxide will transfer to the wash tank 2, and thepressure in the wash tank 2 will rise to approximately 725 psi. Ofcourse, higher or lower pressures are possible, if the cleaning solutionis stored at higher or lower pressures, respectively, inside the centralstorage tank 5. Afterwards, valve 23 is closed again.

In the next step, liquid cleaning solution is transferred to the washtank 2. In an embodiment, liquid carbon dioxide is obtained from thecentral storage tank 5. The central storage tank 5 is connected to thewash tank 2 via lines 112 and 107, fluid displacement unit 1, and lines108. Line 112 is connected to a part of the wash tank 2 where liquidcarbon dioxide accumulates. In line 112, valve 28 is placed. In line108, valve 25 is placed. By opening valves 28 and 25, liquid carbondioxide may be transferred through fluid displacement unit 1 to the washtank 2. The fluid displacement unit 1 then functions as a pump. Pressurein the wash tank may remain at approximately 725 psi.

The amount of liquid carbon dioxide transferred to the wash tank may bedetermined by the time the pumping unit 1 is activated. In anembodiment, the contents in the wash tank may be approximately equal to50% vapor, and 50% liquid carbon dioxide. Other compositions are ofcourse possible. After having transferred a sufficient amount of liquidcarbon dioxide, valves 28 and 25 are closed again.

After bringing an amount of vapor and liquid carbon dioxide into thewash tank 2, the clothes to be cleaned may be washed. Washing may beexerted by continuously pumping cleaning solution, such as liquid carbondioxide through the system. A bottom part of the wash tank 2 isconnected to fluid displacement unit 1 through lines 106 and 107. Valve26 is placed in line 106. As described before, the pump is connected tothe wash tank 2 through line 108, having valve 25. By opening valves 26and 28, and putting into operation pumping unit 1, liquid carbon dioxidefrom the wash tank may be re-circulated through the system. The fluiddisplacement unit 1 then functions as a pump. The clothes to be cleanedmay be thoroughly washed this way. After washing, valves 26 and 28 areclosed again.

After washing, the liquid carbon dioxide may be drained from the washtank 2. In an embodiment, the liquid carbon dioxide is transferred backto the central storage tank 5. This way, the carbon dioxide may bere-used again. Preferably, the relatively dirty liquid carbon dioxidethat is transferred to the central storage tank 5 is cleaned first.

This may be done by transferring the liquid carbon dioxide to a cleaningdevice, such as distillation 6. The liquid carbon dioxide may betransferred from the vessel, through lines 106, 107, to the fluiddisplacement unit 1. From there, it may be transferred to distillation6, through line 109 having valve 27. Transfer may be started by usingfluid displacement unit 1, and opening valves 26 and 29. The fluiddisplacement unit 1 then functions as a pump. After transfer, valves 26and 27 may be closed again. The relatively dirty liquid carbon dioxidewill be distillated, and vapor carbon dioxide will transfer from thedistillation 6 through lines 110, 111 to the central storage tank 5. Thedistillation 6 ensures that a relatively large part of the used carbondioxide may be re-used again, by transferring distillated carbon dioxideto the central storage tank 5. The cleaned carbon dioxide may be avapor. In an embodiment, a cooling unit 8 may be positioned in betweenthe distillation 6 and the central storage tank 5. The cooling unit 8ensures that vapor carbon dioxide is cooled down, such that liquidcarbon dioxide is obtained, which then may be introduced into thecentral storage tank 5. Sludge obtained from the distillation processmay be collected in a sludge collector 7, that is connected to thedistillation 6 through line 118. Sludge may be removed from the systemat point 11, through lines 119, 120, in which a valve 32 may be placed.

After having removed the liquid carbon dioxide, the remaining vaporcarbon dioxide in the wash tank 2 may be removed. Pressure inside thewash tank 2 may still be relatively high, such as 725 psi. The wash tank2 may be depressurized, using the fluid displacement unit 1.Depressurization may be exerted by transferring vapor carbon dioxidefrom the wash tank 2. The transfer of the vapor carbon dioxide willdepressurize the wash tank 2. The vapor carbon dioxide may betransferred, for example, to the distillation 6 where the vapor will becleaned and returned to the central storage tank 5. Transfer of thevapor carbon dioxide may be exerted by using fluid displacement unit 1.Preferably, the pressure of the vapor carbon dioxide is maintained atapproximately 725 psi, to reduce pressure losses within the system. Tothis end, the fluid displacement unit 1 may function as a compressor inthis step.

Finally, the wash tank 2 may be depressurized completely to atmosphericpressure, by opening valve 22 and blowing off the remaining gas in thevessel. Blowing off remaining gas in the vessel will lead to losses ofgas. To prevent losses of gas, the remaining gas might be compressed aswell. However, compressing the remaining gas in the vessel is relativelytime consuming, making the process less efficient. Hence, an optimumbetween time efficiency and material losses is present. Afterdepressurizing the wash tank 2, the clean clothes may be removed.Additionally, a new washing cycle may be started as described before.

The general washing cycle as described before may be expanded withadditional steps to improve the washing result, preservation of carbondioxide, and/or the energy efficiency. These additional steps will bedescribed below.

To improve the washing result, it is possible that several washing stepsare performed. For instance, a series of two washing steps may be used.Cleaning solution, such as liquid carbon dioxide may be brought into thewash tank 2, and clothes may be washed in a first washing step. Afterwashing, the liquid carbon dioxide may be drained from the wash tank 2.Then, another (second) washing step may be performed, by furtherbringing carbon dioxide into the wash tank 2, washing clothes, anddraining the liquid carbon dioxide once again. For the second washingstep, liquid carbon dioxide may be obtained from the central storagetank 5.

The liquid carbon dioxide drained from the first washing step isrelatively dirty. Therefore, it is preferred to clean this liquid carbondioxide by transferring it to the distillation 6, as described before.However, the liquid carbon dioxide drained from the second washing stepis relatively clean, and cleaning this liquid carbon dioxide isrelatively energy consuming, as well as time consuming. Therefore, theliquid carbon dioxide drained is preferably transferred to anintermediate storage 4, where it is temporarily stored for alter use.The intermediate storage 4 is connected to pump 1 through line 113having valve 29. Valve 26 in the wash tank-pump line 106, 107, isopened, together with valve 29. Fluid displacement unit 1 is put intooperation, pumping liquid carbon dioxide from the wash tank 2 to theintermediate storage 4. The fluid displacement unit 1 then functions asa pump. The liquid carbon dioxide from the intermediate storage 4 may beused in a new washing cycle, when bringing liquid carbon dioxide intothe wash tank 2. Thus, instead of using liquid carbon dioxide from thecentral storage tank 5, liquid carbon dioxide obtained from a previouswashing cycle and stored in the intermediate storage 4 is used.

Before the step of pressurizing the wash tank 2 with vapor carbondioxide, the air in the wash tank may be pre-conditioned. Preferably,nitrogen and oxygen are removed from the wash tank 2 in thispre-conditioning step. To this end, a purge tank 3 is connected to thewash tank 2 via lines 101, 102 and valve 21. In the purge tank 3, vaporcarbon dioxide vapor is stored. The vapor carbon dioxide in the purgetank 3 has a pressure of approximately 70-230 psi. The pre-conditioningstep is initiated by opening valve 21, and charging carbon dioxide vaporinto the wash tank 2. The pressure in the wash tank 2 will increase toapproximately 70-230 psi. Afterwards, valve 21 is closed again.Subsequently, valve 22 is opened after charging the wash tank 2 withvapor carbon dioxide. Air inside the wash tank 2 is blown off via line103 to the atmosphere 9. With this, air, and more specifically nitrogenand oxygen are removed from the wash tank 2. As a result, the pressurein the wash tank 2 may be reduced to, for example, atmospheric pressure(14.7 psi). After depressurizing the wash tank 2, valve 22 is closedagain. This step may be used to prepare the wash tank 2 for a followingwashing cycle, by (partially) cleaning the inside of the vessel 2.

After washing, the liquid carbon dioxide and the vapor carbon dioxideneed to be drained from the wash tank 2. As stated before, the liquidcarbon dioxide may be transferred from the wash tank to the intermediatestorage, using fluid displacement unit 1. The vapor carbon dioxideremaining in the wash tank 2, may be removed in two subsequent steps. Inthe first step, vapor carbon dioxide is transferred from the wash tank 2to the distillation 6, using the fluid displacement unit 1. The fluiddisplacement unit decreases the pressure inside the wash tank 2 towardsatmospheric pressure. Preferably, the pressure in the wash tank 2 isreduced to approximately 115 psi. The fluid displacement unit 1 used inthis step may then function as a compressor. The fluid displacement unit1 is arranged for keeping the pressure of the medium transferred atapproximately 725 psi. Hence, the vapor will enter the fluiddisplacement unit at a relatively low pressure, but will be transferredto the distillation 6 with a relatively high pressure. This ensures thatthe pressure side of the system remains at a relatively high pressure(i.e. approximately 725 psi), such that pressure losses and energylosses are prevented.

Once the pressure in the wash tank is reduced to approximately 115 psi,it is possible, in a second step, to transfer the remaining vapor carbondioxide back to the purge tank 3. To this end, the fluid displacementunit 1 is connected to the purge tank 3 through lines 114, 115, and 101.In line 114 a valve 30 is placed. By opening valve 30 and 26, theremaining vapor carbon dioxide may be compressed and transferred towardsthe purge tank 3, using fluid displacement unit 1. The fluiddisplacement unit 1 thus functions as a compressor in this step. In theembodiment shown, a heat exchanger 12 is brought into contact with thewash tank 2. The heat exchanger is arranged for transferring heat fromthe medium (i.e. vapor carbon dioxide) passing through lines 114, 115,to the wash tank 2. Due to the compression action of the fluiddisplacement unit 1, the compressed vapor carbon dioxide will be heated,and this heat may be transferred to the wash tank 2, in order topre-heat the wash tank 2 for a subsequent washing cycle. This step maybe performed until the pressure inside the wash tank 2 is equal toapproximately 30 psi. Then, all valves may be closed again. The washtank 2 may be de-pressurized by blowing off air to the atmosphere byopening valve 22, as described before.

FIG. 2 a shows an embodiment of the fluid displacement device 201. Thefluid displacement device 201 may be a positive-displacement device. Thepositive-displacement device may be a reciprocating device or a pistondevice that uses one or more pistons 205 driven by a crankshaft topressurize fluid. The fluid displacement device 201 comprises an inlet202 connected to a pumping chamber 208, in which a piston 205 isreciprocally movable. The pumping chamber 208 also comprises a dischargeunit 206 connected to an outlet 204. The discharge unit may be aspring-loaded valve. The spring 210 exerts a force in the upstreamdirection, and ensures that the valve 211 is closed. A force in theopposite direction, i.e. the downstream direction, may open the valve211, such that the pumping chamber 208 is in open connection with theoutlet 204. The inlet 202 and discharge unit 206 are positioned atopposite ends of the pumping chamber. It is possible, however, toposition the inlet and the discharge unit at one end of a cylindricalpumping chamber.

In FIGS. 2 a to 2 c, different stages in a working cycle of the fluiddisplacement device are shown. The piston 205 is movable between a firstposition, in which the volume of the pumping chamber 208 is maximal,towards a second position, in which the volume of the pumping chamber208 is minimal. In FIG. 2 a, the piston is in or near the firstposition. In FIG. 2 c, the piston is in, or near the second position.Movement from the first position to the second position is called thecompression stroke. Movement from the second position to the firstposition is called the expansion stroke.

As can be seen in FIG. 2 a, the inlet 202 to the pumping chamber 208 isopen when the piston is in the first position. Fluid may enter thepumping chamber 208 through the inlet 202. Referring to FIG. 2 b, theinlet 202 is closed when the piston 205 moves in the compression stroke.Preferably, the inlet is closed right after the compression stroke hasstarted. Further movement of the piston in the compression stroke pushesthe fluid towards the discharge unit 206. The fluid is compressed duringthe compression stroke, and subsequently pushed through the dischargeunit 206 when the pressure inside the pumping chamber 208 exceeds thepre-set pressure of the discharge unit 206. Since vapor is easilycompressible, the fluid displacement device 201 and the discharge unit206, such as a spring-loaded valve, may be used to compress the vapor.Thus, the discharge unit 206 ensures that the fluid, such as a gas or avapor, may be compressed in order to increase the pressure of the fluid.When liquid is transferred by the piston 205 towards the discharge unit206, the force exerted by the liquid is large enough to open thedischarge unit 206, and the liquid may transfer to the outlet 204. Thusthe fluid may be easily pumped by the fluid displacement device. Afterhaving completed the compression stroke, the piston starts the expansionstroke. BY moving he piston towards the first position, the pressureinside the pumping chamber 208 will decrease. As a result, the dischargeunit 206 is closed. The pumping chamber 208 is now completely closed,such that movement of the piston increases the volume, and subsequentlylowers the pressure. When the piston reaches the first position, thepressure in the pumping chamber is lower than the pressure of the fluidnear the inlet 202 of the fluid displacement device 201. Hence, thefluid, either gas or liquid, is sucked inside the pumping chamber 208,after which another compression stroke may take place. Hence, the fluiddisplacement device is able to function as a pumping/compressing unit,arranged for both pumping and compressing the cleaning solution.

It is possible that additional pumping chambers are provided to thefluid displacement device, each having a respective piston. Additionaldischarge valves may be provided.

In another embodiment a further valve, in particular a one-way valve ispresent upstream from the pumping chamber.

In an embodiment the fluid inlet into the pumping chamber 208 isprovided in the piston, in particular through the piston axle.

In an embodiment the one-way valve upstream from the pumping chamber 208is provided in the piston.

In the drawings and specification, there have been disclosed typicalpreferred embodiments of the invention and, although specific terms areemployed, they are used in a generic and descriptive sense only and notfor purposes of limitation, the scope of the invention being set forthin the following claims.

What is claimed is:
 1. method for washing an article in a dry cleaningsystem employing a cleaning solution, said cleaning solution comprisinga liquid and a vapor, said method comprising: washing in a wash tank anarticle to be washed with said cleaning solution at hyperatmosphericpressure; storing said cleaning solution in a central storage tank,wherein said central storage tank is closeably connected to said washtank; transferring said cleaning solution by a single fluid displacementdevice being a pumping and compressing unit connected through a washtank-pump line to said wash tank for transfer of cleaning solution fromthe wash tank to the fluid displacement device and through a furtherline (108) for transfer of liquid from the fluid displacement device tothe wash tank; the wash-tank line and the further line each closeable bya respective valve (26; 28); wherein the method comprises the steps of:operating said fluid displacement device for transferring of saidcleaning solution in liquid form in said dry cleaning system; operatingsaid same fluid displacement device for depressurizing said wash tank,after removal of the liquid cleaning solution from the wash tank to thecentral storage tank, by removing the vapor from the wash tank by meansof compressing the removed vapor, wherein the fluid displacement deviceis a positive-displacement device, being a reciprocating pump/compressordevice or a piston device to pressurize fluid, arranged for transferringliquid and vapor fluid, and for compressing vapor fluid.
 2. The methodaccording to claim 1, wherein the step of operating said same fluiddisplacement device for depressurizing said wash tank comprises the stepof reducing the pressure in said wash tank towards atmospheric pressure.3. The method according to claim 2, wherein the step of operating saidsame fluid displacement device for depressurizing said wash tankcomprises the step of removing vapor from said wash tank.
 4. The methodaccording to claim 3, wherein the step of operating said same fluiddisplacement device for depressurizing said wash tank comprises the stepof compressing said vapor removed from said wash tank.
 5. The methodaccording to claim 1, wherein the method comprises the steps of:operating said fluid displacement device for pumping said cleaningsolution in liquid form; and operating the fluid displacement device forcompressing said cleaning solution in vapor form.
 6. A method forwashing articles in a dry cleaning system employing a cleaning solution,comprising washing said washing articles in a wash tank at ahyperatmospheric pressure, wherein said dry cleaning system comprises afluid displacement device according to claim 1 for depressurizing saidwash tank towards atmospheric pressure.
 7. A method for washing articlesin a dry cleaning system employing a cleaning solution, comprisingdisplacing and compressing fluids from said dry cleaning system withwashing articles employing a cleaning solution in accordance with afluid displacement device according to claim
 1. 8. The method accordingto claim 1, wherein the fluid displacement device compresses cleaningsolution in vapor form.